In order to take blood pressure it is conventional practice for a doctor (or nurse or other trained operator) to wrap the cuff of a sphygmomanometer around a patient's arm. He then utilizes one hand to inflate the cuff by means of a squeeze bulb to impede the flow of blood to the arm, while with his other hand he holds the sensor of a stethoscope on the patient's arm to monitor heart pulses acoustically. Using his first hand, the doctor then slowly bleeds air from the cuff to gradually decrease the pressure in the cuff while carefully observing the pressure gauge (aneroid or mercury column) of the sphygmomanometer. As the pressure in the cuff decreases he observes and mentally retains the pressure gauge readings at which the first heart pulse is heard (systolic pressure) and at which the heart pulses cease to be heard (diastolic pressure). It is common for the doctor or operator to repeat this process one or more times either to confirm the initial readings in the event that he may not have been able to clearly detect the systolic and diastolic pressure points, or to minimize the ambiguity of this type of measuring system, or to average the results, or to re-affirm the results in the event of loss of trend of concentration or failure to recall one or both of the observed readings.
It is also clear that owing to the inherent lack of precision with this type of medical measurement system, the results vary significantly from operator to operator. Additionally, as conventionally configured and utilized, this instrument is slow, necessitates much subjective judgement in interpreting the results, is cumbersome to use, and does not easily adapt itself for use by an average patient in taking his own blood pressure.